<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>test</title>
  <style>
    .box{
      width: 800px;
      height: 800px;
      background-color: yellow;
    }
    .box1{
      width: 50%;
      height: 10%;
      background-color: red;
    }
  </style>
</head>
<body>
<div class="box">
  <div class="box1"></div>
</div>
</body>
</html>